In upright thermal CVD device that performs processes such as forming Si3N4 film on the multiple substrates by utilizing dichlorosilane (SiH2Cl2) and ammonia (NH3), other than the silicon nitride (Si3N4) film comprising the target film, byproducts such as ammonium chloride (NH4Cl) are generated and adhere to low temperature sections such as the wall surface inside the furnace opening at the lower section of the reaction furnace. These adhering byproducts are a source of particles and create problems. One method for resolving this problem is a technique for heating low temperature sections such as the furnace opening on the lower section of the reaction furnace to an extent where the byproducts will not adhere (see for example Japanese Patent Non-Examined Publication No. 2002-184769).
However, there are temperature limits even on this heating method due to the O-ring for sealing between the reaction furnace and the furnace opening seal cap for sealing the reaction furnace, and the rotation mechanism for rotating the boat inside the reaction furnace in the vicinity of the furnace opening. Technology is therefore required for preventing byproducts such as NH4Cl from adhering to low temperature sections such as the furnace opening, without heating.
In order to resolve the above problems with the prior art, the present invention has the object of preventing byproducts such as NH4Cl from adhering to low temperature sections such as the furnace opening, without applying heat.